The invention relates to a process making it possible to produce composite material connections for structures having at least two bars interconnected by at least one connecting joint, so as to form a lattice or a lattice element. The invention also relates to a lattice obtained by performing the said process.
In the present context the term "lattice" means an assembly of at least two bars interconnected by connecting junctions or joints, so as to form between the said bars one or more meshes, which can be open or closed by a skin.
In addition, the term "lattice element" means an elementary structure having two bars interconnected by a connecting joint.
The lattice-type structures obtained by performing the process according to the invention can be used in numerous industrial fields such as aviation and cars. Thus, in the aeronautical industry, it is possible to use these structures as canopy frames for cockpits or as door frames, e.g. on helicopters or certain aircraft.
In the present state of the art, there are numerous processes making it possible to produce lattice-type structures, which are both rigid and light and which can have different geometries imposed by the numerous applications to which such structures apply.
A known solution consists of using thin metal profiles or metal elements formed from stamped thin sheets assembled by welding, bonding, riveting or any other conventional process. Another known solution consists of using composite material elements obtained by thermoforming or roto-moulding, followed by the assembly thereof by bonding or welding.
Another known method consists of producing composite material elements by draping or winding and interconnecting said elements by metal connecting joints, the connection between the composite material elements and the metal connecting joints being obtained either by draping the composite materials onto the joints and at least in part on the bars, or by bonding the bars to the connecting joints. Such connections do not have a guarantee of continuity of the materials forming them over their entire path between the individual bars.
All these production processes require complex and very accurate tools in order to produce the constituent components of the final lattice-like structure, followed by further complex and very accurate tools in order to carry out the series assembly of these various components, whilst ensuring a good shape reproducibility.
Moreover, in order to comply with the requirements as regards to the rigidity of the lattice structures which it is wished to produce, it is often necessary to use local reinforcements, such as metal brackets or selective reinforcements of high strength fibre-based laminates, in order to locally increase the curvature. In the case of the third aforementioned method using draping operations, the production of such local reinforcements in non-developable structures makes it necessary to place in the latter separate textile reinforcing elements, which have to be cut, put into place and superimposed so as to provide a reinforcement corresponding to the final shape of the structure to be produced. However, the cuts which must then be made in the textile reinforcing elements introduce discontinuities in the fibres, which also leads to areas of reduced strength in the thus obtained composite material structure. For safety reasons, this is unacceptable in a certain number of applications, such as aeronautical applications. Moreover, these cutting operations take a long time .and are expensive and their performance has relatively limited reproducibility and reliability characteristics.